The present invention relates to a process for preparing low color 2,3-epoxypropyltrialkylammonium halide, and more particularly, low color 2,3-epoxypropyltrimethylammonium chloride.
Various methods for preparing 2,3-epoxypropyltrimethylammonium chloride are known in the art. However, these known processes yield a product which is yellow in color to various degrees. Some of these methods are described hereinafter.
James D. McClure, J. Org. Chem., Vol.35,No. 6,pp. 2059-2061 (1970), describes a process for the preparation of glycidyltrimethylammonium chloride by reacting epichlorohydrin with trimethylamine. The reaction is illustrated by the following equation: ##STR1## This reaction is best carried out in an aprotic solvent such as ethers, ketones, and esters in which 2,3-epoxypropyltrimethylammonium chloride is insoluble. An excess of epichlorohydrin can be used as solvent as well. Preparation of 2,3-epoxytrimethylpropylammonium bromide by reacting epibromohydrin with trimethylamine is also described in this article.
U.S. Pat. No. 3,475,458 (J. D. McClure) discloses the preparation of crystalline glycidyltrimethylammonium chloride of high epoxide level, useful in the production of starch ethers, by reacting epichlorohydrin and trimethylamine in a solvent selected from saturated hydrocarbon ether, lower alkyl ketone, lower alkyl alkanoate and chlorofom-hydrocarbon mixtures.
U.S. Pat. No. 4,066,673 (J. B. Doughty et al) discloses a process for the preparation of 1,2-epoxy propyl trialkylamine chloride in a methanol solution. Epichlorohydrin is first dissolved in methanol and then a stoichiometric amount of trialkylamine (for example, trimethylamine or triethylamine) in methanol is slowly added thereto.
It is also known to prepare 2,3-epoxypropyltrimethylammonium chloride by a method which involves reacting epoxy compounds, particularly epichlorohydrin, with an acid salt of a trialkylamine, particularly trimethylamine hydrochloride, in aqueous media, followed by treatment with caustic. This method is illustrated by the following equations: ##STR2##
The use of 2,3-epoxypropyltrimethylammonium chloride for preparing cationic starch ethers is also well known. Some of the processes for preparing cationic starch ethers are described hereinafter.
U.S. Pat. No. 2,876,217 (E. F. Paschall) discloses a process for the preparation of starch ethers containing quaternary ammonium substituents by reacting starch with the reaction product of epihalohydrin and a tertiary amine or a tertiary amine salt. The epihalohydrintriethylamine reaction product is obtained by mixing triethylamine and epihalohydrin with water. After agitating the reaction solution for 5 hours at room temperature, the solution is concentrated to a thick syrup under a vacuum. This epihalohydrintriethylamine syrup is added to an alkaline aqueous slurry of starch. The reaction mass is then neutralized with acid and the cationized starch ether recovered.
U.S. Pat. No. 3,346,563 (P. R. Shildneck et al) discloses a process for the preparation of a cationic starch ether by reacting starch and a quaternary halohydrin salt with an alkaline catalyst, the halohydrin being obtained by reacting hypohalous acid with allyl quaternary halide salt of a tertiary amine. This process, is represented by the following equation: ##STR3## It was postulated that, in the presence of the alkali, an intermediate reaction takes place by which the halohydroxypropyl quaternary ammonium ether is cycled to form in situ the epoxide and that this epoxide reacts with starch.
2,3-Epoxypropyltrialkylammonium halides are reactive cationic quaternary amines. They are readily reactive with most substrates, charged or uncharged, to impart to it a permanent cationic charge. Examples of suitable substrate include, for example, natural cellulosic materials such as starch, flour, guar gum, as well as synthetic materials such as cellulose ethers, polyvinyl alcohol and polymers. In particular, 2,3-epoxypropyltrimethylammonium chloride has been widely commercially used in the manufacture of cationic starches.
2,3-Epoxypropyltrialkylammonium halides also suitably impart a permanent cationic charge to various fibers. Suitable fibers include: (i) natural and regenerated cellulosic fibers such as, for example, cotton, linen, and viscose rayon; (ii) natural and regenerated protein fibers such as, for example, wool, cashmere, and casein; (iii) regenerated fibers such as, for example, cellulose acetate, and cellulose triacetate; (iv) synthetic fibers such as, for example polyamide, polyester, and polyacrylonitrile.
In addition to 2,3-epoxypropyltrialkylammonium halides aqueous solutions of about 50% to about 70% active 3-chloro-2-hydroxylpropyltrimethylammonium chloride are commercially available for use as quaternizing agents. When this type of the quaternizing agent is used, caustic or other base must be utilized to first convert it to its epoxy form since it is the epoxy form of the quaternizing agent that is the active species for most reactions.
One particular use for these quaternizing agents as reacted with alkaline starch is in the manufacture of paper. The cationic starch is added in the wet-end of a paper process and functions primarily as a dry strength additive. The cationic starch maintains its charge throughout the entire pH range, so that it is usable in acid, neutral, and alkaline paper-making processes. It functions like a charged glue to hold the paper fibers together, and is believed to improve sheet strength by promoting fiber bonding through a combination of ionic bonding with the essentially anionic cellulosic substrates, and also hydrogen bonding. It also finds use in conjunction with internal sizing agents, including alkenyl succinic anhydride ("ASA") and alkylketene dimer ("AKD"), in fine paper applications.
However, in the paper manufacture color and brightness are important qualities. Therefore, raw materials used in production are desirably colorless or of extremely low color. Unfortunately, widely used conventional direct reaction of epichlorohydrin with trimethylamine produces 2,3-epoxypropyltrimethylammonium chloride which has a strong yellow color. When this product is used to make cationic starch, the yellow color may be imparted to the cationic starch and thus to the final paper product. The color of 2,3-epoxypropyltrimethylammonium chloride can be reduced slightly by lowering the temperature or increasing the ratio of epichlorohydrin to trimethylamine which are reacted to form the 2,3-epoxypropyltrimethylammonium chloride. However, both of these alternatives increase capital and operating costs, and the lower temperatures also slow down the reaction. Increasing the epichlorohydrin to trimethylamine ratio also tends to reduce yield and require more recycle epichlorohydrin for a given reactor.
There is a perceived need in the industry for the 2,3-epoxypropyltrialkylammonium halide product which is devoid of color or has reduced color so that, upon application, less color is imparted to the cationic starch and thence to the paper, or other, final product.